Transcriptome Profiling, Biochemical and Physiological Analyses Provide New Insights towards Drought Tolerance in Nicotiana tabacum L.

Drought stress is one of the main factors limiting crop production, which provokes a number of changes in plants at physiological, anatomical, biochemical and molecular level. To unravel the various mechanisms underpinning tobacco (Nicotiana tabacum L.) drought stress tolerance, we conducted a comprehensive physiological, anatomical, biochemical and transcriptome analyses of three tobacco cultivars (i.e., HongHuaDaJinYuan (H), NC55 (N) and Yun Yan-100 (Y)) seedlings that had been exposed to drought stress. As a result, H maintained higher growth in term of less reduction in plant fresh weight, dry weight and chlorophyll content as compared with N and Y. Anatomical studies unveiled that drought stress had little effect on H by maintaining proper leaf anatomy while there were significant changes in the leaf anatomy of N and Y. Similarly, H among the three varieties was the least affected variety under drought stress, with more proline content accumulation and a powerful antioxidant defense system, which mitigates the negative impacts of reactive oxygen species. The transcriptomic analysis showed that the differential genes expression between HongHuaDaJinYuan, NC55 and Yun Yan-100 were enriched in the functions of plant hormone signal transduction, starch and sucrose metabolism, and arginine and proline metabolism. Compared to N and Y, the differentially expressed genes of H displayed enhanced expression in the corresponding pathways under drought stress. Together, our findings offer insights that H was more tolerant than the other two varieties, as evidenced at physiological, biochemical, anatomical and molecular level. These findings can help us to enhance our understanding of the molecular mechanisms through the networks of various metabolic pathways mediating drought stress adaptation in tobacco.

Integrated analysis of transcriptomic and metabolomic data reveals critical metabolic pathways involved in polyphenol biosynthesis in Nicotiana tabacum under chilling stress.

Chilling stress increases the amount of polyphenols, especially lignin, which protects tobacco (Nicotiana tabacum L. cv. k326) from chilling stress. To clarify the molecular biosynthesis mechanism of the key representative compounds, specifically lignin, RNA sequencing and ultra-high pressure liquid chromatography coupled to quadrupole-time of flight mass spectrometry technologies were used to construct transcriptomic and metabolomic libraries from the leaves of tobacco plants subjected to normal (25°C) and chilling (4°C) temperature treatments. Transcriptomic libraries from the different samples were sequenced, generating more than 40million raw reads. Among nine samples, metabolomic analysis identified a total of 97 encoding enzymes that function in the key steps of pathways related to polyphenol biosynthesis, where 42 metabolites were also located. An integrated analysis of metabolic and transcriptomic data revealed that most of the intermediate metabolites and enzymes related to lignin biosynthesis were synthesised in the leaves under chilling stress, which suggests that the biosynthesis of lignin plays an important role in the response of tobacco leaves to cold temperatures. In addition, the cold insensitivity of chalcone synthase genes might be considered to be an important rate-limiting factor in the process of precursor substance flow to flavonoid biosynthesis under chilling stress. Furthermore, the upregulated expression of phenylalanine ammonia lyase (PAL), hydroxycinnamoyl transferase (HCT) and cinnamyl-alcohol dehydrogenase (CAD) under chilling stress is the key to an increase in lignin synthesis. This study provides a hypothetical basis for the screening of new active metabolites and the metabolic engineering of polyphenols in tobacco.

The effects of plastic film mulching on maize growth and water use in dry and rainy years in Northeast China.

Plastic film mulching (PM) has been widely used to improve maize (Zea mays L.) yields and water use efficiency (WUE) in Northeast China, but the effects of PM in a changing climate characterized by highly variable precipitation are not well understood. Six site-year field experiments were conducted in the dry and rainy years to investigate the effects of PM on maize growth, grain yield, and WUE in Northeast China. Compared to crops grown without PM treatment (control, CK), PM significantly increased the grain yield by 15-26% in the dry years, but no significant yield increase was observed in the rainy years. Yield increase in the dry years was mainly due to a large increase in dry matter accumulation pre-silking compared to the CK, which resulted from a greater dry matter accumulation rate due to the higher topsoil temperature and water content. As a result, the WUE of the crops that underwent PM (3.27 kg m(-3)) treatment was also increased by around 16% compared to the CK, although the overall evapotranspiration was similar between the two treatments. In the rainy years, due to frequent precipitation and scant sunshine, the topsoil temperature and water content in the field that received PM treatment was improved only at some stages and failed to cause higher dry matter accumulation, except at the 8th leaf stage. Consequently, the grain yield and WUE were not improved by PM in the rainy years. In addition, we found that PM caused leaf senescence at the late growth stage in both dry and rainy years. Therefore, in practice, PM should be applied cautiously, especially when in-season precipitation is taken into account.